Tracking Issue for array_methods

This is a tracking issue for a couple of basic methods on arrays. The feature gate for the issue is #![feature(array_methods)]. Currently, this includes the following methods:

as_slice, as_mut_slice Add [T; N]::as_[mut_]slice #76120
each_ref, each_mut Add [T; N]::each_ref and [T; N]::each_mut #75490

Note: these methods were all collected under the same array_methods feature name as I suspect many (often small) methods to be added to array in the near future. Creating a new feature and tracking issue for each seems overkill. We can still split off some methods into dedicated features later, if required.

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also uses as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

Decide what set of methods to stabilize in the first round
Change feature names of all methods that are not yet stabilized to something specific
Adjust documentation (see instructions on rustc-dev-guide)
Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

Use the names each_ref and each_mut or change it to something else? Alternatives: each_as_ref/each_as_mut, as_refs/as_mut_refs. See PR Add [T; N]::each_ref and [T; N]::each_mut #75490 for the name discussion.

Just for the protocol, I plan to add the following methods in the near future:

cloned, copied and unzip: blocked by figuring out how we best add additional impl blocks for arrays (e.g. [&T; N] where T: Clone)
zip: waiting for add array::FillError similar to array::IntoIter #75717 or Add 'core::array::from_fn' and 'core::array::try_from_fn' #75644 to get merged; otherwise this method would add duplicate code already added in Added [T; N]::zip() #79451

(discussions about the usefulness of those method should be had in the dedicated PR threads and not here)

Rollup merge of rust-lang#76120 - LukasKalbertodt:add-as-slice-method…

@LukasKalbertodt

@LukasKalbertodt I have opened PR #79451 for zip, saw your comment just now.

With regards to stabilization I think as_slice, as_mut_slice could be stabilized first.

I think they are much more useful than the others in this tracking issue. These are already common methods for existing data types so it's not a new API.

I sometimes find myself running into cases where Deref coercion doesn't work and I need this. Currently I'm using &arr[..] which doesn't really communicate well why it is needed.

For example

// io::Read does something like this
trait Trait {}
impl Trait for &[u8] {}
impl<T: Trait + ?Sized> Trait for &mut T {}

fn takes_trait(t: impl Trait) {}

fn main() {
    let mut arr = [0, 1, 2, 3];
    
    // currently
    takes_trait(&mut &arr[..]);
    
    // with `.as_slice()` its nice and clear
    takes_trait(&mut arr.as_slice());
    
    // can't use deref coercion in this case
    takes_trait(&mut &arr);
    //          ^^^^^^^^^ the trait `Trait` is not implemented for `&[u8; 4]`
}

@rossmacarthur

I agree with @rossmacarthur and would like to propose stabilizing as_slice and as_mut_slice. These methods exist on many other types throughout std (e.g. Vec) and I can't think of a reason to wait with stabilization. I can't see how the name or semantics would still change. And I'm pretty sure we want those methods.

Partial stabilization is up: #88353

Any news about this?

🔔 This is now entering its final comment period, as per the review above. 🔔

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

Rollup merge of rust-lang#103522 - Dylan-DPC:76118/array-methods-stab…

Unrolled build for rust-lang#103522

Less unsafe with array_methods

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Tracking Issue for array_methods #76118

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LukasKalbertodt commented on Aug 30, 2020

usbalbin commented on Nov 29, 2020

rossmacarthur commented on May 11, 2021

LukasKalbertodt commented on Jun 23, 2021

jhpratt commented on Aug 26, 2021

21 remaining items

pravic commented on Oct 20, 2023

rfcbot commented on Jan 16, 2024

rfcbot commented on Jan 26, 2024

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Tracking Issue for `array_methods` #76118